The invention relates to an apparatus and method for depositing a uniform coating on a planar surface. More particularly, the invention relates to a method and apparatus for depositing a uniform coating on a planar surface using multiple plasma sources. Even more particularly, the invention relates to a method and apparatus for depositing a uniform coating on a planar surface by injecting reactant gases through a common injection system into a plurality of plasmas that are generated by multiple expanding thermal plasma sources.
Plasma sources are capable of depositing a large variety of coatings, such as transparent abrasion resistant coatings, transparent UV-filtering coatings, and multi-layer coating packages on a substrate at a high deposition rate. In such deposition processes, a reactant gas interacts with a plasma to form species that are deposited on the substrate. Individual plasma sources, such as expanding thermal plasma (also referred to hereinafter as “ETP”) sources, can be used to uniformly coat areas having a diameter in the range of about 10–15 cm.
An array of multiple plasma sources may be used to coat larger substrate areas. Such large area coating work typically deals with depositing a coating on macroscopically flat—or planar—surfaces. To achieve a uniform coating on such planar surfaces, the multiple plasma sources may be spaced in a two-dimensional pattern, such as a linear or zigzag array.
When multiple plasma sources are used to coat large areas, reactant gas is typically provided to each plasma source by a separate delivery system; i.e., each plasma source has an individual reactant gas source that requires individual flow control. When scaling plasma deposition technology up to coat surfaces having larger dimensions, however, the use of the individual reactant sources and flow controllers may cause significant variability in the coating process and a resulting decrease in coating uniformity. In addition, as the number of plasma sources used in the coating process increases, the cost to equip each plasma source with an individual delivery system and flow control becomes significant.
An array of multiple plasma sources in which each plasma source has an individual reactant gas injector system is unable to uniformly coat large planar surfaces and is uneconomical. Therefore, what is needed is a method and apparatus for uniformly coating a large area, planar substrate using multiple plasma sources.